解释

if 语句里面包含真和非真，但是如果我们没有写清楚真和非真的话，会如何呢？

if(x)

相当于

if(x != 0)

如果是指针的话，相当于

if(x != NULL)

而

if(1)

相当于

if(1 != 0)

还有

if(0)

相当于

if(0 != 0)

举个例子

#include<stdio.h>
int main()
{int x = 2;printf("x value:%d\n",x);printf("code:'x==2'\nvalue:%d\n" ,x==2);printf("code:'x!=2'\nvalue:%d\n" ,x!=2);printf("code:'x=3'\nvalue:%d\n" ,x=3);printf("code:'x-1'\nvalue:%d\n" ,x-1);printf("code:'!x'\nvalue:%d\n" ,!x);printf("code:'!1'\nvalue:%d\n" ,!1);printf("code:'!0'\nvalue:%d\n" ,!0);printf("code:'x'\nvalue:%d\n" ,x);printf("\n");if(0){printf("if(0) is running!\n");}if(1){printf("if(1) is running!\n");}if(x){printf("if(x) is running!\n");}if(x = 0){printf("if(x = 0) is running!\n");}if(x = 1){printf("if(x = 1) is running!\n");}return 0;
}

输出结果

x value:2
code:'x==2'
value:1
code:'x!=2'
value:0
code:'x=3'
value:3
code:'x-1'
value:2
code:'!x'
value:0
code:'!1'
value:0
code:'!0'
value:1
code:'x'
value:3if(1) is running!
if(x) is running!
if(x = 1) is running!

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